 I tend to think it would be hard for a person to remember if they did hear a song 50 years later. But they're different as well. And the song overall is nothing like Stairway to Heaven, but it is some sort of derivative work. Zeppelin beat the case in 2016, but it was appealed in 2018, revived, and then the U.S. Supreme Court could have heard it. But they decided not to, effectively killing the lawsuit. There are countless other examples of court cases like this.